The opsins

Genome Biol. 2005;6(3):213. doi: 10.1186/gb-2005-6-3-213. Epub 2005 Mar 1.


The photosensitive molecule rhodopsin and its relatives consist of a protein moiety - an opsin - and a non-protein moiety - the chromophore retinal. Opsins, which are G-protein-coupled receptors (GPCRs), are found in animals, and more than a thousand have been identified so far. Detailed molecular phylogenetic analyses show that the opsin family is divided into seven subfamilies, which correspond well to functional classifications within the family: the vertebrate visual (transducin-coupled) and non-visual opsin subfamily, the encephalopsin/tmt-opsin subfamily, the Gq-coupled opsin/melanopsin subfamily, the Go-coupled opsin subfamily, the neuropsin subfamily, the peropsin subfamily and the retinal photoisomerase subfamily. The subfamilies diversified before the deuterostomes (including vertebrates) split from the protostomes (most invertebrates), suggesting that a common animal ancestor had multiple opsin genes. Opsins have a seven-transmembrane structure similar to that of other GPCRs, but are distinguished by a lysine residue that is a retinal-binding site in the seventh helix. Accumulated evidence suggests that most opsins act as pigments that activate G proteins in a light-dependent manner in both visual and non-visual systems, whereas a few serve as retinal photoisomerases, generating the chromophore used by other opsins, and some opsins have unknown functions.

Publication types

  • Research Support, Non-U.S. Gov't
  • Review

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Binding Sites
  • Cattle
  • Conserved Sequence
  • Evolution, Molecular
  • Humans
  • Models, Molecular
  • Multigene Family / genetics
  • Multigene Family / physiology*
  • Phylogeny
  • Protein Conformation
  • Rod Opsins / chemistry
  • Rod Opsins / genetics
  • Rod Opsins / physiology*


  • Rod Opsins